It's still a move within the family, so to speak: Both suppliers are a part of the Toyota group, with Toyota owning nearly a quarter of their shares. Still, in the relatively rigid personnel system of large Japanese companies, this counts as a major break with tradition.

"Suppliers work with multiple auto makers around the world," Mr. Mizushima told reporters in Nagoya on Friday. "It could be that parts makers have better knowledge in certain areas... I think this move is intended so that Toyota can manufacture and send out products that can truly be accepted globally."